Leaf: Opposite on stem, length 9" to 16", pinnately compound with seven to 11 yellowish-green leaflets each 4" to 5 1/2" long, oblong in shape, and not stalked except the terminal leaflet; terminal bud is large and pointed; leaves smooth on both surfaces; turn yellow to brown in autumn.
For more information see
http://www.dnr.state.mn.us/trees_shrubs/deciduous/blackash.html.